Currently LTE-A (Long Term Evolution-Advanced) system can support CA (Carrier Aggregation) of at most 5 carriers and a LTE-A UE (User Equipment, namely, user terminal) needs to submit ACK (ACKnowledgement)/NACK (Non-ACKnowledgement) feedback information of corresponding multiple downlink carriers and downlink subframes in the same uplink subframe. Therefore, LTE-A system defines a new kind of PUCCH (Physical Uplink Control Channel) format, namely, PUCCH format 3 to support transmission with comparatively large ACK/NACK feedback bit number.
PUCCH format 3 supports to feed back at most 20-bit ACK/NACK and its transmission structure is shown in FIG. 1. Firstly ACK/NACK feedback bits are encoded using RM (Reed-Muller) coding. In case the number of ACK/NACK feedback bits is not larger than 11 bits, RM (32, O)+repetition coding method in Rel-8 (Release-8, version 8) system is reused to encode ACK/NACK feedback bits into 48-bit coded bits. While in case the number of ACK/NACK feedback bits exceeds 11, Dual-RM coding method is used to divide ACK/NACK feedback bits into two groups equally, and RM (32, O)+truncation coding method is adopted for each group to encode ACK/NACK feedback bit in each group into 24-bit coded bits. The coded bits sequence after RM encoding will be scrambled at a bit-level and modulated and transmitted in 2 slots of an uplink subframe by spreading the modulated symbols into multiple SC-FDMA (Single Carrier-Frequency Division Multiple Access) symbols in a slot through a time domain OC (Orthogonal Cover) sequence with a SF (Spreading Factor) equal to 5, so as to achieve time domain diversity gain. For normal cyclic prefix (Normal CP), there are two columns of RS (Reference Signal, also called pilot frequency) in each slot and they occupy the second SC-FDMA symbol and the six one respectively, as shown in FIG. 1; for extended cyclic prefix (Extended CP), there is one column of RS, which occupies the fourth SC-FDMA, as shown in FIG. 2. The same information shall be transmitted in two slots using frequency hopping transmission, which means that each slot occupies one of the two marginal parts of frequency band respectively to enable, so as to achieve frequency domain diversity gain.
PUCCH format 3 also supports shortened format for transmitting SRS (Sounding Reference Signal) at the same time. In shortened format, the length of SF in the first slot is 5, that of SF in the second slot is 4, the last SC-FDMA symbol in the second slot is reserved for transmitting SRS and its structure is shown in FIG. 3. If UE is configured to support simultaneous transmission of ACK/NACK and SRS in the same uplink subframe, shortened PUCCH format 3 will be used to transmit multi-bit ACK/NACK together with SRS. Table 1 shows the OC sequences corresponding to different SF lengths and NSFPUCCH therein represents SF length. Considering that the different data used different OC sequences to do time domain spreading are orthogonal with each other, thus, multiplexing transmission of multiple UEs in the same PRB (Physics Resource Block pair) pair can be supported by configuring different OC sequences for different UEs and at most 5 users can be multiplexed in a PRB pair.
TABLE 1OC Sequence of PUCCH Format 3SequenceOrthogonal sequence [wnoc (0) . . . wnoc (NSFPUCCH − 1)]index nocNSFPUCCH = 5NSFPUCCH = 40[1 1 1 1 1][+1 +1 +1 +1]1[1 ej2π/5 ej4π/5 ej6π/5 ej8π/5][+1 −1 +1 −1]2[1 ej4π/5 ej8π/5 ej2π/5 ej6π/5][+1 −1 −1 +1]3[1 ej6π/5 ej2π/5 ej8π/5 ej4π/5][+1 +1 −1 −1]4[1 ej8π/5 ej6π/5 ej4π/5 ej2π/5]—
A base station informs a UE the PUCCH format 3 resource index nPUCCH(3) used for ACK/NACK feedback via PUCCH format 3 through explicit signaling and UE will calculate the PRB number (nPRB) and the OC sequence number (nOC) for feeding back ACK/NACK message according to the PUCCH format 3 resource index, that is
                              n          PRB                =                  {                                                                      ⌊                                      m                    ⁢                                          /                                        ⁢                    2                                    ⌋                                                                                                  if                    ⁢                                                                                  ⁢                                          (                                              m                        +                                                                              n                            s                                                    ⁢                                                                                                          ⁢                          mod                          ⁢                                                                                                          ⁢                          2                                                                    )                                        ⁢                    mod                    ⁢                                                                                  ⁢                    2                                    =                  0                                                                                                                          N                    RB                    UL                                    -                  1                  -                                      ⌊                                          m                      ⁢                                              /                                            ⁢                      2                                        ⌋                                                                                                                    if                    ⁢                                                                                  ⁢                                          (                                              m                        +                                                                              n                            s                                                    ⁢                                                                                                          ⁢                          mod                          ⁢                                                                                                          ⁢                          2                                                                    )                                        ⁢                    mod                    ⁢                                                                                  ⁢                    2                                    =                  1                                                                                        [        1        ]            
Wherein, NRBUL refers to uplink bandwidth (measured through PRB quantity) of the primary carrier, m=└nPUCCH(3)/NSF,0PUCCH┘, wherein NSF,0PUCCH refers to the SF length in the first slot and ns is the index of slot in a radio frame; and nOC=g(nPUCCH(3)), wherein detail form of g(□) has not been determined yet.
Different from the PUCCH format 1/1a/1b in LTE Rel-8 system, each RE (Resource Element) in a SC-FDMA symbol in the PUCCH format 3 corresponds to a different modulation symbol, that is, frequency-domain spreading is not used, and different user data are distinguished by orthogonal method only through the time domain OC sequence. In case different UE in the same frequency domain resource in adjacent cells use the same OC sequence, transmitted data of multi-user will interfere with each other, and such adjacent cell interference is very serious particularly to the cell edge users. And PUCCH demodulation performance of target cell users will be directly influenced if the user's transmit power in interfered cell is great.
In the procedure of realizing the objects of the present invention, at least the following defects existing in the prior art were found:
Currently in LTE-A system, the existing PUCCH format 3 transmission program cannot solve the inter-cell interference in case of multiple UEs in different cells using the same OC sequence on the same resource.